Use the EC for any external clock, freeing up RA6 as an i/o pin. I'm
pretty sure the LP, HS, XT settings are to configure hardware inside
the PIC for the ranges of crystals attached across Osc1 and Osc2
eg 32kHz, 4MHz, 20MHz types. The different xtals need their own type
of drive. Although an external clock into Osc1 can be used when HS is
set, HS doesn't free up Osc2 as i/o

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